1. Field of the Invention
The present invention relates to encoding of computer generated images and in particular, but not exclusively, for encoding animated scenes presented on interactive systems.
Such systems need to operate in real-time whilst producing acceptable quality images. Within the constraints of consumer systems, where cost limits the available processor power, techniques for efficiently coding image planes are required to enable real time recreation of images from a limited data stream. In the case of compact disc based systems, the disc typically outputs a 150 Kb per second data stream of which 20 Kb is reserved for sound. At a visually acceptable screen refresh rate, this allows around 8Kb per image frame for image coding.
2. Description of the Related Art
Various techniques have been proposed for reducing the information needed to code an image frame including separating an image into areas of relatively high and relatively low spatial density with a more complex, information-intensive, coding being applied to detailed higher density areas of the image than is applied to the lower density areas. Such a technique is described in EP-A-0358498 which also reduces data requirements by coding the lower resolution (video chrominance) components at half the rate of the higher resolution (luminance) components, that is to say for each display pixel, the chrominance information will be refreshed in every other image frame whereas the luminance information is refreshed every frame.